1. Field of the Invention
This invention relates to debugging processes in microprocessors, and particularly to a method for creating trace triggers from non-concurrent events.
2. Description of Background
When signals within a microprocessor chip (or other logic) are not properly driven, the microprocessor does not behave correctly. The debugging process (i.e., finding and fixing the problem) becomes simpler when the signals in the chip can be observed. To make this possible, trace mechanisms are implemented to record events that occur on these internal signals. However, trace mechanisms can only capture a limited amount of information. Once a trace buffer is full, additional information may not be recorded without overwriting older information. Trigger mechanisms are usually added to give more control over when events get recorded.
Triggers are programmed to look for specific events of interest, such as a signal or a pattern on a bus. When a desired event is found, the trigger activates, telling the trace mechanism to either start or stop recording. Conventional triggers watch for a combination of concurrent events, leaving limited flexibility in defining trigger events. An inherent limitation of existing solutions is that this concurrent nature prevents triggering off of multiple events that reach the triggers in sequential order. Designers have to make sure signals used to form an event reach the trigger mechanism simultaneously. To do this, components referred to as staging latches are added in order to delay signals so they arrive at the trigger mechanism concurrently. For instance, if half of an address gets to the trigger mechanism a cycle before the other half, the designer would have to delay the first half with staging latches so that the trigger could observe the entire address simultaneously. These staging latches add power and area, and rigidly define the concurrent signal relationships that define events.
Considering the limitations of the above-mentioned trigger mechanisms, it is desirable, therefore, to formulate a highly flexible method and apparatus for creating trace triggers from non-concurrent events while reducing the need for staging latches.